Improvements in gas fired furnaces and boilers have resulted in high efficiency systems in small packages. At the same time, environmental regulations for reduction of combustion byproducts have increased. To cope with both of these conditions, gas appliance manufacturers have requested low cost, low profile induced draft blowers to fit into the smaller volumes, to improve efficiency, and to meet the environmental requirements. A further trend in induced draft blowers will be to provide variable speed capability to allow continuous optimization of combustion and to provide blower systems that are in themselves efficient and that produce low electromagnetic interference.
A single-phase brushless DC motor consisting of a four pole stator and a four pole permanent magnet rotor has been determined to be the most economical motor to satisfy the foregoing requirements. However, a problem common with single phase motor commutation schemes occurs when the windings are de-energized and the motor comes to rest at a magnetically neutral position. This position, where the rotor magnets center themselves about the path of least reluctance, is also the point at which the motor torque constant is zero. Regardless of the current applied to the motor winding, the rotor will remain in the neutral position, and will not start.
Gas regulatory agencies require residential combustion systems utilizing a combustion (or induced draft) air supply blower to include a sensor to confirm that the blower is in operation before the actuation of the gas supply valve. Previously, this has been accomplished by the use of a pressure transducer. The brushless motor control electronics offer a convenient means to confirm operation of the motor and fan, eliminating the need and cost of the pressure transducer. Some regulatory agencies, however, will not recognize operation of the motor as assuring operation of the impeller because of the typical shaft linkage between the motor rotor and the impeller.
There is clearly a need in the art for an integrated motor and impeller assembly for use as an air moving blower product which has a low profile and utilizes a motor with simplified and economical motor commutation electronics and positive starting characteristics.